Composition and process for electroplating bright nickel



United States Patent O COMPOSITION AND PROCESS FOR ELECTRO- PLATING BRIGHT NICKEL Charles L. Faust and William H. Safraneic, Columbus, Ohio, assignors, by mesne assignments, to Rockwell Spring and Axle Company, Coraopolis, Pa., a corporation of Pennsylvania N Drawing. Application July 20, 1953, Serial No. 369,224

8 Claims. (Cl. 204- 43) This invention relates to nickel electroplating. In particular, this invention relates to a leveling and bright-tobrilliant mirrorlike nickel electroplate, and to a method or process and a composition useful in producing such plate. Specifically, this invention relates to the continuous and reproducible electrodeposition of nickel as a bright-to-brilliant mirrorlike, hard, adherent, and ductile metal, characterized by its ability to cover surface imperfections, such as scratches, etc., to achieve leveling.

The terms bright and mirrorlike mean, respectively, reflective and reflective without image distortion, when applied to the ductile plates produced in connection. with this invention. Leveling may be defined as the property of filling in the surface depressions of the basis metal during deposition so that the resulting plate has a planar surface not exhibiting or duplicating the rough surfaces of the underlying basis material.

In the metal-finishing art, mirrorlike metallic surfaces are desired which are adherent to the base, are free from blemishes of appearance, ofier protection to the basis metal, and are tarnish-resistant. Many of these surfaces are obtained with nickel plates over basis metals, such as steel, brass, zinc, and aluminum die castings, etc. For an excellent quality and appearance, it has been the ,usual practice to eliminate defects in the basis metal surface, first by polishing and/or bufiing. The cost of preparing the surface by such finishing operations is somewhat proportional to the quality of final appearance. Where the best appearance and colorare desired, extra polishing and bufiing operations are required, but these are expensive.

For the puipose of minimizing these operations and costs,

bright metal coating and plating methods have been developed and are in commercial use, particularly for nickel, copper, and zinc plates. Even so, such plating methods, and the so-called bright plates produced thereby, are notoriously dependent upon the highest quality of polishing and buffing of the basis material before plating,

and/or on buifing and coloring the plate. Otherwise, surface scratches and defects readily show through the plate. Hence, although the. plates are brilliantly lustrous, they do not hide the surface defects. The degree of hiding varies somewhat according to the plating conditions, but none of the prior-art plates. give a high degree of covering, so as to eliminate the necessity of bufling. and coloring operations after plating.

Moreover, where parts are later to be chromium plated, and only rarely is it otherwise, subsequent buifing in the case of nickel electroplate requires extra handling. and double racking. Further, when the nickel plate is buffed to produce a high quality mirror finish, it appears gray in certain angles of reflected light because of the fine coloring scratches, which are unavoidable regardless of the skill of the operator. The finish, thus, is directional in color tone. In addition, all of the patented or commercially practiced processes for the' production buffed.

"ice

of bright nickel plates fail to provide plates with a duetility which is satisfactory for general applications.

The variations and importance of polishing details and technique form a skilled art in themselves, expensive to apply. For example, the customary bright nickel plating practices for steel (or other basis materials) require polishing and bufiing through the following sequence of operations:

1. Rough polish on wheels or belts with grit sizes of 40 to 80, depending on the starting roughness of the surface.

2. Polish through a succession of operations using progressively finer grit sizes on abrasive wheels or belts, for example, and ISO-grit.

3. Continue polishing with 240- and 320-grit abrasive.

4., Buff with a fine abrasive which breaks down to finer-than-400 grit.

5. Finally, after plating, color-buff on wheels having an extremely fine compound.

The planeness of surfaces is measured in terms of root mean square microinches. The levelness of roughpolished surfaces (step 1) lies within the range of about 30 to 60 R. M. S. microinches, depending on the pressure applied and the grit size. Step 2 produces surfaces in the range of about 10 to 30 R. M. S. microinches, depending on pressure, number of passes, hardness of the abrasive and condition of wheels or belts. The polishing of step 3 results in a surface levelness in the range of about 4 to 10 R. M. S. microinches.

If polished steel has an R. M. S. value of 23 microinches (.l80-grit polish) and is subsequently plated with nickel using a prior-art, so-called bright-nickel method,

the plated finish measures 19 R. M. S. microinches. On

the other hand, if the as-full-bright-plated surface is to have a 9 R. M. S. rnicroinch finish, desired as final, the basis metal must first be finished to 9 or 10 R. M. S. microinches before plating by one of the known brightnickel processes, or the bright plate must be subsequently It is obvious, then, that elimination of steps 3, 4 and 5, is a much sought-after goal in metal finishing.

Attempts have been made to develop processes that produce a plate which is not only bright but also has the property of smoothening out original surface irregularitiesso that they are no longer noticeable after plating. For example, British Patent No. 622,761, June 5, 1949, describes a nickel-plating procedure utilizing cournarin as an addition agent in nickel-plating baths for depositing a nickel coating which levels the basis metal surface byplating more metal in depressions than in the relief areas of the surface. Thus, a filling in or leveling effect is accomplished and the polishing and buffing work on the basis metal can be supplanted by a less costly electrodeposition. Unfortunately, not all buffing is eliminated, because this nickel-plating method results in a semibright plate which needs subsequent costly bufiing to obtain full brilliance. For example, the surface of the plate produced by the teachings'of the British patent is not of full color in terms of the art, being only semibright, and has a roughness of 18 R. M. S. microinches over steel with an original finish of 34 R. M. S. microinches.

With special conditions, the plates produced by the process of this British patent can be made sufficiently bright to require no subsequent mechanical buffing. However, the special conditions required are impractical to reproduce commercially. Moreover, the consumption of the coumarin, resulting from volatilization and decomposition, is so excessive' when these unusual conditions are applied, that the cost of maintaining a proper concentration of coumarin in the bath exceeds the savings in the elimination of the polishing and buffing steps prior to and after plating. Also, the ductility of plates is reduced to an unsatisfactory condition.

Although metal salt additions, per se, have not yet been disclosed as providing the means for producing ductile plates with good smoothening or leveling action, such salts have been added to nickel baths containing other additives in an efiort to achieve increased brightness and consequent reduction in the costs of bufiing and coloring operations. For example, U. S. Patents Nos. 2,112,818 and 2,114,006 disclose that additions of zinc or cadmium salts, together with an organic-type addition agent of the class represented by naphthalene sulfonic acid, yield bright plates. However, such plates do not have the property of leveling, or filling in, or smoothening surface irregularities, to the extent necessary to produce leveling and bright-to-brilliant mirrorlike plates, or to reduce polishing costs. The plated surface levelness is not appreciably different from the levelness of the basis metal or starting surface. For example, the average R. M. S. microinch reading on a representative 0.0015- inch thick plate produced by the process disclosed in U. S. Patent No. 2,112,818 was 28 over steel measuring 34 R. M. S. microinches, and 23 over steel measuring 27 R. M. S. microinches.

The use of cobalt sulfate as a brightening agent in combination with nickel formate and formaldehyde has been disclosed in U. S. Patent No. 2,026,718. However, this combination of addition agents also fails to provide the means for producing plates withrthe improved power of leveling surface irregularities. A plate produced by this process, 0.0015-inch in thickness, had an R. M. S. value of 20 microinches over steel originally measuring 22 R. M. S. microinches, and 33 R. M. S. microinches over steel originally measuring 36 R. M. S. microinches.

U. S. Patent 2,191,813 discloses the combination of zinc or cadmium and sulfonimide or a sulfonamide for brightening nickel plate. However, it has been found that such plate failed to smoothen or fill in surface irregularities in the basis metal, as determined by measurements with a surface roughness gauge.

In U. S. Patent No. 2,467,580, sulfonated phenyl and naphthyl sulfones are described as addition agents forI producing bright nickel plate. Semibright nickel plate was obtained by duplicating the procedures disclosed in that patent, but such plate required bufiing to produce a full-bright appearance.

The combination of phenyl sulfones with certain alkyl pyridium and quinolinium pyrazoles was disclosed in U. S. Patent No. 2,513,280, but this combination of addition agents results only in a semibright plate which re quires buffing to obtain a full-bright appearance.

it is obvious that a plating process, which not only levels by filling in surface scratches so that the resulting plate is nondirectional in color tone but also produces a brilliant, bright-to-brilliant mirrorlike plate, requiring no further finishing, is adherent, corrosion-resistant, and ductile, and which can be economically and satisfactorily operated on a batch or continuous basis without appreciable loss of reagents due to decomposition and volatilization, would be ofgreat industrial importance.

It is, therefore, an object of this invention to provide a method for electrodepositing nickel as a uniform brightto-brilliant mirrorlike plate characterized by the ability to level surface irregularities to a degree never achieved before, and which is corrosion-resistant, adherent, protects the basis metal against corrosion, is ductile, is hard, and does not require subsequent buffing or coloring to enhance its appearance or brilliance.

It is a further object of this invention to provide a composition of matter useful in a method for electrodepositing nickel plate having the aforementioned improved 'qualities.

It is another object of this invention to provide an electrodeposited leveling and bright-to-brilliant mirrorlike nickel plate having the above improved qualities.

These and other objects and advantages of the present invention will become more apparent from the following detailed description and examples.

It has now been found that ductile and leveling nickel electroplates having a bright-to-brilliant mirrorlike appearance may be produced by passing an electric current through an agitated bath containing a major amount of a nickel salt and additionally minor amounts of sulfonated phthalide or sulfonated naphthalide and a salt of at least one metal selected from the group consisting of zinc, cadmium and thallium. Moreover, the resulting plates are adherent, are corrosion-resistant, protect the underlying basis metal against corrosion, and are ductile.

The aqueous electrolytic bath is acidic and contains dissolved therein a suitable nickel salt, an inorganic salt of at least one additive metal selected from the group consisting of zinc, cadmium, and thallium, and sulfonated phthalide or sulfonated naphthalide. The nickel salts predominate in the bath since the plates to be produced consist predominantly of nickel. Only sufiicient additive metal salt and sulfonated phthalide or naphthalide compound are added to produce the level and bright-tobrilliant mirrorlike plates of this invention. Desirably, the bath should also contain a buffer and a wetting agent. An electric current is then passed through the bath from an anode to a cathode to create sufficient current density at the anode and cathode, while the bath is agitated and heated, to effect satisfactory results. The plate, as deposited from this electrolytic bath, is a level and brightto-brilliant mirrorlike plate of nickel, or nickel and atleast one of the above additive metals.

Very minor amounts of impurities are probably present in the electrodeposited coating and bath of this invention. However, they do not appear to materially affect the resulting nickel plate.

Whenever, due to a change in the amount of bath constituents or in operating conditions, an increase in the nickel content of the plate occurs, there will be a corresponding decrease in the codeposited metal or metals content so that there are always essentially only two elements present, i. e., nickel and the codeposited metal or metals, in cases'where more than one metal additive is present in the bath. Likewise, where there is a decrease in the nickel content, there will occur an increase in the codeposited metal or metal content of the plate. By varying the bath constituents and factors or operating conditions, as will be hereinafter more clearly set forth, it is possible to deposit coatings containing a large amount of metal additive, as, for example, up to about 7% zinc, and the balance nickel. The plates as electrodeposited will be corrosion-resistant, ductile, leveling, and will vary from bright to brilliant, mirrorlike, having R. M. S. values of 5 microinches or below, on basis metal having a surface roughness of 13 R. M. S. microinches or more.

Any suitable salt may be used in the bath which will "result in a nickel plate under acid-plating conditions.

Most suitable salts are nickel fluoborate, nickel chloride, nickel sulfamate, and/ or nickel sulfate. Any orall of these salts may'be used in the same bath, but it is preferred, for ease of control, best efficiency and results, to use baths containing a chloride salt, a fluoborate salt, or a mixture of chloride and sulfate salts.

The nickel chloride salt used is preferably hydrated nickel chloride (NiClz-6Hz0). However, NiClz can likewise be used, although allowance for lack of water of crystallization should be made.

The nickel fluoborate added to the bath is generally obtainable in the form of a concentrated solution containing 40 to nickel fluoborate (Ni(BF4)2)..

. The nickelsulfate. generally used is NiSO4-6Hz0.

The amount of nickel, per se, added to the bath should be in sufficiently large quantity toprovide aplate having the desired high nickel content and properties for decorative and protective purposes with respect to the basis material which is usually steel. This amount can vary from 17 g./l. up to saturation which is about 233 g./l. Expressed in another way, this range is equivalent to from 75 to 1000 g./l. of nickel sulfate (NiSOr-6H2O) plus from 25 to 60 g./l. of nickel chloride (NiCl2'6H2O). For consistently best results, from standpoint of economy, ease of control, and plate condition, it is preferred to use from 34 to 120 g./l. of nickel, corresponding to from 150 to 480 g./l. of nickel sulfate, plus from 30 to 60 g./l. of nickel chloride. Thus, it is seen from the above that the nature and concentration of the nickel salts are not critical.

The additive metals, hereinbefore listed, are codeposited with the nickel, resulting in nickel-rich plates having a better protective value than commercially pure nickel plates. The amount of additive metal, per se, to be added to the bath can range from 0.1 to 1.0 g./l., and the proportion'of the second codeposited metal found in the plate may vary from as little as 0.1% up to about 7%. It is to be understood that additive or codeposited metal can mean combinations of more than one of'the above metals.

The additive metals are added to the plating baths in the form of inorganic or organic salts or compounds having generally the same nonmetallic radicals as described above with respect to the nickel salts. Representative examples of salts of these metals are cadmium chloride (CdCl2 and CdC1z'2--l/2HzO), cadmium sulfate (CdSOi, 3CdSO4-8H2O and CdSO4-4H2O), cadmium fiuoborate (Cd(BF4)z), zinc chloride (ZnClz), zinc sulfate (211804, ZnSO4-6H2O and ZnSO4-7HzO), zinc fluoborate (Zn(BF4)z), monothallium chloride (TlCl),

trithallium chloride (TlCl3-TlCl3-H2O), thallium sesquichloride (TlzCls), thallous hydroxide (TlOH), thallous sulfate (T1250 4), and thallous acid sulfate (TlHSOr).

The other halide salts (bromides, fluorides and iodides) of the additive metals could be used. However, they are generally impractical in the baths of the present invention due to their cost, corrosive activity, etc.

The metals, as their salts, may be added to the. bath singly or in mixtures to provide plates containing nickel and one or more of the codepositing metals.

The codepositing metal salt may have an anion different from that of the nickel salt. Thus, where nickel sulfate is used, it is notnecessary to use, for example, zinc sulfate, but zinc chloride or fluoborate can readily be used without impairment of operating conditions or results. In addition, when more than one additive metal is used, it is not necessary to use salts of the same type. For example, zinc sulfate and cadmium chloride can be mixed together and used in the same bath.

The structural formulae of phthalide and naphthal'ide, before sulfonation, are as follows:

Phthalide B 'Naphthalide a Naphthalide When these compounds are sulfonated, the acid radical (SOsH) will take various positions on the rings, depending on the position of the directing groups. The product of sulfonating phthalide is probably a mixture of 4- phthalide sulfonic acid and 6-phthalide sulfonic acid. The product of sulfonating a or fi-naphthalide is probably a mixture of 6- and 9-naphthalide sulfonic acids.

The sulfonic acids of. phthalide and naphthalideneed not be isolated from the excess sulfuric acid required for sulfonation. The excess acid is neutralized with a suitable base or basic salt, such as sodium hydroxide, nickel carbonate, or zinc oxide.

It is also possible to use the salts of the sulfonic acids and the crude sulfonation products, as well as the sulfonic acids themselves, and such materials are to be included in the terms sulfonated phthalide or sulfonated naphthalide. The sodium salts are prepared by mixing the sulfonation products in cold brine solution followed by filtering and recrystallizing.

Phthalide may be sulfonated by heating for two hours at l20 C. with five parts by weight of 20 per cent fuming sulfuric acid. The sodium salt is isolated. by pouring the product in cold brine. The yield is about per cent.

As has been previously pointed out, only small amounts of thesulfonated' materials need be added to the bath to produce the required results. While very large amounts can be used, they do not appreciably alter the results and, in some cases, might even be detrimental. The amount used should be equivalent to from 2 to 20 g./l. of sulfonated phthalide.

A buffer is usually added to the acid nickel-plating baths to prevent sudden changes in the pH which would adversely affect results. Bufiers customarily used in the art can be added to the baths disclosed herein, in amounts to properly effect the buffering action. It has been found best to employ boric acid. From a practical standpoint, the amount of buffer generally used will vary from 10 to 60 g./l., although best results in control, economy, and plate condition are obtained with concentrations of from 30 to 45 g./l. It will be noted that the concentrated solutions of nickel fluoborate that are commercially furnished usually contain about 1 to 3 per cent by weight of boric acid as a stabilizer. In very carefully controlled plating operations using fiuoborate salts, this amount of boric acid will be sufiicient, although for most purposes it is always advisable to add more boric acid as a buffer.

A wetting agent is desirable to prevent pitting of the plates and is generally used in the baths of this invention. Agents previously known to prevent pitting in nickel plates will be satisfactory. It will be understood, however, that such agent must not adversely affect the baths, operating conditions or resulting electroplates. An example of a suitable Wetting agent is sodium lauryl sulfate. Only a minor amount need be added to the bath to prevent pitting, and large amounts are unnecessary and wasteful. Usually, from 0.1 to 1 g./l. of the wetting agent can be present in the bath, although from 0.2 to 0.5 g./l. is more satisfactory for preventing pitting of the surfaces. I i

The pH of the bath is adjusted by adding to the bath a suitable alkali such as nickel carbonate, nickel hydroxide, or zinc oxide. The pH of the bath should always be on 'theacid side and desirably should not exceed about 5 for any appreciable period of time. It should never be below about 1.9 or the bath will be thrown outof balance,

and the composition, levelness and brightness of the plates will be adversely altered on continued operation. It has been found that the best bath stability and resulting plate condition are accomplished by maintaining the pH of the bath from 2.5 to 4.5.

The electrolytic baths used to make the level and brightto-brilliant mirrorlike plates of this invention can be prepared by any method. No particular order of addition of reagents to the solution, or water, is required. Thus, all of the ingredients can be mixed together in the dry state and then added to the water to provide the proper concentrations. They can also be added singly in any order to the water. After all of the essential reagents have been added or are in solution, the pH of the bath can then be adjusted by appropriate additions of suitable acids or bases.

The baths should always be agitated during plating in order to consistently obtain leveling plates having a bright-to-brilliant mirror-like appearance. The work itself may be moved, or paddles or propellers may be used to stir up the electrolyte. The agitation should be sufficient to set up a flow in the bath so as to keep the composition of the bath substantially constant at all points and particularly at or near the face of the work being plated.

Alloy anodes can be used which contain from 0.1 to per cent by weight of an additive metal, the balance being nickel. However, nickel anodes are preferred. Current densities for the anodes can range from 5 to 60 amp./ sq. ft. It is preferred to maintain the current density of the anodes within the range of from 20 to 40 amp/sq. ft. in order to obtain the best results from a commercial viewpoint.

The customary methods known to the art for cleaning, degreasing and pickling are used in preparing a basis metallic (or nonmetallic) surface, the cathode, for receiving the leveling and 'bright-to-brilliant mirrorlike nickel plate of this invention. When the surface cathode is in a cleaned condition, it is then plated with the metal. The articles to be plated, as cathodes, can be made of iron, steel, copper, brass, zinc, zinc die castings or alloys, magnesium, and aluminum, etc., as well as many other materials normally used for platings of nickel for protective and/or decorative purposes. Desirably, basis materials, such as aluminum, magnesium, and zinc, should also be strike-plated with copper, brass, etc., by prior-art methods before depositing thereon the bright plate of this invention. This additional step is unnecessary, when plating on iron, steel, copper or brass.

Operating cathode current densities of from 20 to 1% or more amp/sq. ft. can be used in the present method to produce bright-to-brilliant mirrorlike nickel plates, although from a practical or commercial standpoint it has been found best to employ current densities in the range of from 30 to 60 amp/sq. ft.

To obtain mirror-bright plates, it is only necessary to plate for five minutes. However, for a good leveling elfect at least minutes operation is necessary. The

plating time can be continued for as long as needed,

although for economy and entirely satisfactory results, plating times are not generally continued beyond 60 minutes.

The bright plating baths disclosed herein are heated during operations to obtain the desired plates. They are operable and stable over long periods of time at the lowest practical operating temperature of about 100 F. up to at least 165 F. For general commercial use, the preferred temperature range is from 125 to 145 F.

Minor amounts of impurities may be present in the bath and resulting plate, as previously mentioned. However, while not absolutely necessary, it is naturally desirable that the materials used in the process disclosed herein should be substantially pure in order to decrease the amount of possible contaminants and to. consistentlyobtain reproducible results.

Certain materials are consumed during the plating operation. For example, the nickel or nickel alloy anodes must be inspected at regular intervals and replaced before being entirely exhausted to prevent disruption of the bath stability. It the anodes are unalloyed nickel, the. cadmium, zinc, and/ or thallium consumed in fixed ratio with the nickel is replaced by making regular additions to the bath of suitable cadmium, zinc, and/or thallium salts. The only other appreciable losses occurring from the electroplating operation will be some loss of minor amounts of the bath constituents removed in the solution film clinging to the plated work. These small dragout losses can readily be controlled by periodic checks of the bath constituents which will indicate the amount of constituent needed to maintain the bath in the proper balance and within the desired operating ranges. Thus, the bath can be continuously operated, and, generally, it is only necessary to replace the soluble anodes, if used, or bath constituents if insoluble anodes are used.

Concentration of undesirable reagents or chemicals do not build up or precipitate in the bath during the process, thus avoiding any slowing down of the plating operations, by impairing the plates or requiring that the bath be dumped and entirely replaced with new materials. However, filtration may be desirable, as with most electroplating processes, to remove dirt and other insolubles that may form or be added to the bath by the Work. It should be noted here, that cadmium and zinc are generally most harmful impurities in the prior-art bright nickel-plating baths because they darken the plate and cause it to be dull and/or brittle. In the baths constituting this new invention, these metals are desirable and beneficial addition agents and should not be removed from the bath. Furthermore, several other metallic impurities that are harmful in the prior-art bright plating baths can be tolerated without harmful effects in the plating baths constituting this invention. Examples of such metals are antimony, chromium, lead, iron, manganese, mercury, molybdenum, phosphorus, selenium, tallurium, and tungsten.

It is understood, of course, that by varying the current density, agitation, and temperature, the composition of the electroplates can be changed somewhat, although within the ranges of concentration of chemical constituents and operating conditions as described herein, leveling and bright-to-brilliant mirrorlike nickel coatings will be readily produced.

Most generally, the dense, ductile, nondirectional, uniform, level and bright-to-brillian mirrorlike plates of this invention will be desired for decorative and protective purposes, relying upon their appearance without any further plating or finishing operations. However, if it is so desired, other bright metals, such as bright chromium, which protects the color of the nickel under adverse conditions, can be deposited directly on the bright metal plate from plating baths well known to the art. The bath of the present invention has excellent throwing power and attributes for electrodepositing bright-to-brillian mirrorlike nickel in a wide range of compositions, and the process can be practiced for other purposes than merely decorative or protective plating. Thick plates, for example, 0.03() inch have been satisfactorily deposited with mirrorlike appearance and without treeing or roughness.

The following example will serve to illustrate the invention with more particularity to those skilled in the art.

A plating bath was formulated as follows:

Components Amount Nickel sulfate (NiSO4-6Hz0) 360 g.!l. Nickel chloride (NiClz-bHgO)--. 30 g./l. Boric acid (H3BO3) 42 g./l. Zinc sulfate (ZnSOMH O); 2.0 g./1. Sodium salt of sulfonated'phthalide 5.0 g./l. XXXD, a solution of sodium lauryl sulfate 1.0 percent, by volume.

made by the Harshaw Chemical Co. Water The pH of the bath was 3.1. The bath was agitated with a paddle and its temperature was 135 F. The cathode current density was 50 amp./ sq. ft. and the anode current density was about 20 amp/sq. ft. Steel, polished with 40-, 80-, 120- and ISO-grit abrasive coated belts and having a finish measuring 13 R. M. S. microinches, was smoothened to R. M. S. microinches by plating for 40 minutes. The appearance of the plate was mirrorlike.

From the above example, it is apparent that much filling and smoothing is accomplished. An improvement of about 60 per cent in the reduction of roughness was obtained. Thus, by the novel method of this invention, steel polished through lSO-grit dry finishes, without additional polishing, bufiing, or color bufling, can now be nickel plated to a clear, mirrorlike appearance, showing practical elimination of the finishing grit scratches in the basis metal.

Plates produced by the process of this invention withstand approximately twice the distortion by bending before breaking occurs when compared with the bright nickel plates of the prior art.

The present leveling and bright-to-brilliant mirrorlike plates, as electrodeposited, thus represent decided improvements in the art of nickel plating. Moreover, the plated surface produced according tothe present process, requires no mechanical buffing after plating. Hence, it is superior in appearance being the same at all angles of inspection, and it not only saves in finishing costs but produces a surface of uniform and superior lustre and color richness, which is alo transmitted to any subsequently applied decorative chromium or other metal plate. The plates produced by the process disclosed herein have better ductility than the plates produced by commercially practiced bright-plating processes; they do not chip, crack, peel or separate from the basis material under repeated flexing or edge rubbing. Furthermore, the plates of this invention exhibit better corrosion protection than plates produced by prior-art bright nickelplating methods, especially in salt spray-fog tests.

The desirable and novel results, particularly leveling, brightness, and ductility, as are now achieved by the present invention, depend upon the previously unpredictable utility of the combination of two unlike types of addition agents, (1) the salts of zinc, cadmium, and/or thallium, and (2) sulfonated phthalide or a sulfonated naphthalide, neither of which alone provides the combination of brightness, good leveling and good ductility that is obtained by using the methods of the present invention.

In summary, this invention teaches that the addition to the usual nickel plating baths of sulfonated phthalide or sulfonated naphthalide and salts of at least one metal selected from the group consisting of zinc, cadmium, and thallium, will result in leveling and bright to mirrorbright plates which are adherent, corrosion resistant, and ductile. Moreover, such baths can be operated on a batch or continuous basis with negligible loss of the sulfonated phthalide or naphthalide under practical operating conditions, which is of great industrial importance. Furthermore, plates produced by the disclosed method can be directly overplated with chromium without any need for subsequent mechanical bufling, thus maintaining the color and protective qualities of the nickel plate without the directional scratches which are caused by mechanical bufling.

The invention is not limited to the preferred embodiment but may be otherwise embodied or practiced within the scope of the following claims.

We claim:

nickel electroplate which comprises an acidic solution of a major amount of nickel, an organic material selected from the group consisting of sulfonated phthalide and sulfonated naphthalide in an amount equivalent to at least 2 g./l. sulfonated phthalide and from 0.1 to 1.0 g./l. of a metal selected from the group consisting of zinc, cadmium and thallium.

2. A composition of matter for depositing a bright nickel electroplate consisting essentially of an acidic solution of from 17 to 233 g./l. nickel, an organic material selected from the group consisting of sulfonated phthalide and sulfonated naphthalide, said organic material in an amount equivalent to from 2 to 20 g./l. sulfonated phthalide, and from 0.1 to 1.0 g./l. of a metal selected from the group consisting of zinc, cadmium and thallium.

3. A composition of matter for depositing a bright nickel electroplate consisting essentially of an acidic solution of from 17 to 233 g./l. nickel, an organic material selected from the group consisting of sulfonated phthalide and naphthalide, said organic material in an amount equivalent to from 2 to 20 g./l. sulfonated phthalide, from 0.1 to 1.0 g./l. of a metal selected from the group consisting of zinc, cadmium and thallium, a butter and a wetting agent.

4. The composition according to claim 3 in which the pH is from 1.9 to 5.0.

5. In the process of depositing a bright nickel electroplate, the step of passing an electric current through an electrolyte between an anode and a cathode, said electrolyte comprising an acidic solution of a major amount of nickel, an organic material selected from the group consisting of sulfonated phthalide and sulfonated naphthalide in an amount equivalent to at least 2 g./l. sulfonated phthalide and from 0.1 to 1.0 g./l. of a metal selected from the group consisting of zinc, cadmium and thallium.

6. In the process of depositing a bright nickel electroplate, the step of passing an electric current through an electrolyte between an anode and a cathode, said electrolyte consisting essentially of an acidic solution of from 17 to 233 g./l. nickel, an organic material selected from the group consisting of sulfonated phthalide and sulfonated naphthalide, said organic material in an amount equivalent to from 2 to 20 g./l. sulfonated phthalide, and from 0.1 to 1.0 g./l. of a metal selected from the group consisting of zinc, cadmium and thallium.

7. In the process of depositing a bright nickel electroplate, the step of passing an electric current through an electrolyte between an anode and a cathode, said electrolyte consisting essentially of an acidic solution of from 17 to 233 g./l. nickel, an organic material selected from the group consisting of sulfonated phthalide and naphthalide, said organic material in an amount equivalent to from 2 to 20 g./l. sulfonated phthalide, and from 0.1 to 1.0 g./l. of a metal selected from the group consisting of zinc, cadmium and thallium, a buffer and a wetting agent.

8. In the process of depositing a bright nickel electroplate, the steps of passing an electric current through an electrolyte between an anode and a cathode, said electrolyte consisting essentially of an acidic solution of from 17 to 233 g./l. nickel, an organic material selected from the group consisting of sulfonated phthalide and naphthalide, said organic material in an amount equivalent to from 2 to 20 g./l. sulfonated phthalide, from 0.1 to 1.0 g./1. of a metal selected from the group consisting of zinc, cadmium and thallium, a butter and a wetting agent, and agitating said electrolyte during deposition.

References Cited in the file of this patent UNITED STATES PATENTS 2,112,818 Waite Mar. 29, 1938 

1. A COMPOSITION OF MATTER FOR DEPOSITING A BRIGHT NICKEL ELECTROPLATE WHICH COMPRISES AN ACIDIC SOLUTION OF A MAJOR AMOUNT OF NICKEL, AN ORGANIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF SULFONATED PHTHALIDE AND SULFONATED NAPHTHALIDE IN AN AMOUNT EQUIVALENT TO AT LEAST 2 G./L. SULFONATED PHTHALIDE AND FROM 0.1 TO 1.0 G./L. OF A METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM AND THALLIUM. 